The present invention relates to a control apparatus for a serial printer which prints character font data of a dot matrix form and, more particularly, to a control apparatus for a printer which prints both a standard character and an expanded character (an expanded character herein includes a character obtained by simply expanding a standard character several times and a character which is expanded and modified, e.g., rotated) during one-line printing.
When a conventional serial printer completes a printing operation for one line, a predetermined amount of paper, corresponding to a line pitch, is fed, thus sequentially performing printing for each line. For this reason, when the amount of paper fed is controlled, an expanded character having a height several times that of a standard character can be printed. For example, when an expanded character having a height of 48 dots is printed using a printing head of 24-dot height, a 48-dot character is divided into two 24-dot zones, and respective zones are continuously printed without vertical separation. In other words, an upper 24-dot zone of the expanded character is printed first, paper is fed by a 24-dot height, and thereafter a lower 24-dot zone thereof is printed.
When both standard and expanded characters are printed during one-line printing, over- and under-justified printing can be performed by controlling the timing at which character data is developed in a line buffer. However, middle-justified printing cannot be performed simply by controlling a supply timing of data to the line buffer. In order to overcome this drawback, a reverse paper feed mechanism can be provided in a printer. However, since precision in the amount of paper fed cannot be maintained, a printed output is easily shifted, and the structure of a printer becomes complex, thus increasing costs.
When an expanded character is printed and the number of print dots is excessively increased, printing duty may exceed rated power and power consumption may also exceed a rated range. For example, when an underline having a 2-dot height is expanded 16 times, an underline of a 32-dot height is obtained. When this underline is printed using a printing head having a 24-dot height, all the dot printing elements are simultaneously turned on. In addition, in order to draw the underline, these elements must be continuously turned on. Therefore, power consumption is greatly increased and exceeds rated power. In order to overcome this, the capacity of a power source can be increased so as to cope even when all the dot printing elements of the printing head are simultaneously and continuously turned on. However, in this case, the power source, i.e., the overall structure of the printer becomes large in size and expensive.
Furthermore, in a conventional printer, as a printing direction mode, so-called double and single direction modes can be freely selected. In the double direction mode, printing for two lines is performed by reciprocating (moving in forward and reverse directions) the printing head, and in the single direction mode, printing is performed by moving the printing head only in the forward direction. However, when an expanded character is to be printed and the double direction mode is selected, printed dots may be shifted due to a precision error in a paper feed mechanism, thus degrading printing precision. For this reason, when the expanded character is printed, the double direction mode is not preferred. On the other hand, since a standard character is printed during one-movement of the head, when the standard character is printed, printing shift will not occur when the double direction mode is selected. Thus, in view of printing speed, the double direction mode is preferably selected for the printing of a standard character. Even when an expanded character is printed, if printing quality can be neglected, such as a test printing, the double direction mode can be selected for high-speed printing. Conventionally, printing modes are manually selected by a user, resulting in inconvenience due to an erroneous selection.